But if Trump can’t control his tantrums once he’s sworn in on Friday, it becomes downright dangerous.

What if an enemy – say North Korean dictator Kim Jong Un – provokes the new president by testing a missile capable of striking the U.S. mainland? Will Trump talk to his national security advisers, consult with South Korea and Japan and develop a strong yet measured response? Or will he immediately launch a war of words that could lead to a real military confrontation?

Statesmanship may be beyond Trump’s capacity, but his inability to act at least somewhat presidential was on full display in his assault on Lewis.

Premium content for only $0.99

The 30-year congressman said that he did not consider Trump a “legitimate” president because of Russian interference in the election, and that he would not attend Friday’s inauguration. It’s a bold statement, but not completely out of bounds.

Trump could have stayed above the fray, as President Barack Obama did when Trump questioned his legitimacy, or merely expressed disappointment as did Vice President-elect Mike Pence.

Instead, Trump went on the offensive, tweeting Saturday: “Congressman John Lewis should spend more time on fixing and helping his district, which is in horrible shape and falling apart. … All talk, talk, talk – no action or results. Sad!”

What’s pathetic is how Trump continues to ignore history and the facts. First, the Atlanta-area district Lewis represents includes corporate headquarters, Emory University and some suburbs as well as poor neighborhoods. Second, Lewis has a record of eloquent words and courageous action. As a student activist, he spoke at the March on Washington in 1963. He was also jailed and beaten multiple times, most graphically while trying to cross the Edmund Pettus Bridge in Selma in 1965.

In a follow-up tweet, Trump repeated his racist and ignorant view that America’s inner cities are “burning and crime infested” ghettos.

Trump’s tweets were the last straw for a growing number of Democrats, two dozen-plus and counting, who are joining Lewis in boycotting the inauguration. They include Reps. Judy Chu, Mark DeSaulnier, Jared Huffman, Barbara Lee, Ted Lieu, Zoe Lofgren, Lucille Roybal-Allard, Mark Takano and Maxine Waters of California.

We’re not sure it’s the right response. Even if you don’t support the man, you have to respect the office. But this is not a normal transition of power, so it is understandable.

As he becomes our 45th president, Trump should be uniting the nation, as he promised to do on election night.

Instead, he is further dividing it and raising more doubts about his readiness to lead.

President-elect Donald Trump on Wednesday delivered his first press conference since the November presidential election. Trump addressed his relationship with Russia and how he will handle his business once taking office.